ARID1A (AT-rich interactive domain-containing protein 1A), also known as BAF250a, is a recently identified tumor suppressor that is a component of the SWI/SNF chromatin remodeling complex. ARID1A functions by binding AT-rich DNA sequences to regulate gene expression of nucleosome mobilization and chromatin processes. While ARID1A is typically expressed in most normal tissues, it is frequently mutated in a multitude of tumors, including breast, lung, gastric, renal and ovarian cancers.

Genomic sequencing revealed that most ARID1A mutations are truncating mutations, and the presence of mutations is highly correlative with loss of ARID1A protein expression by immunohistochemistry. Deficient ARID1A expression was observed in approximately 70% of renal cell carcinomas, 50% of gastric cancers, 40% of clear cell ovarian carcinomas, and 40% of endometrioid carcinomas. Furthermore, loss of ARID1A expression was determined as an independent marker for poor prognosis; tumors were correlated with higher stage and grade, are more likely to be chemoresistant, and associated with shorter progression-free and overall survival rates. ARID1A antibody may be used for identifying ARID1A defect tumors.